Modulation of protein macromolecules controlling muscle membrane conductances: The acetylcholine receptor and the voltage-gated sodium channel of muscle membrane are the best characterized of the proteins controlling membrane conductances and are, thus, excellent models to study basic biophysical phenomena. Preliminary experiments indicate that cholinergic channel parameters are modified in chick myocytes grown in cholesterol-enriched media. We will use patch clamp methods to measure receptor channel conductance and open time parameters and correlate them with cholesterol to phospholipids ratios in these myocytes membranes. We have also observed that extracts from ciguatoxic barracuda, one of the tropical fish implicated in human intoxication with ciguatera, inhibit the action of acetylcholine in the frog neuromuscular junction. Experiments are proposed to study the mechanism of this inhibition in the frog motor endplate. Using chromatographically purified ciguatoxic fractions we will intracellularly record membrane potentials and measure sodium currents under patch clamp. Patches of chick myocyte membrane will be clamped to assay effect of these fractions on acetylcholine receptor properties. These experiments are designed to bring us closer to an understanding of the mechanisms by which these macromolecules control membrane excitability. Minority students participating in these studies will learn modern electrophysiological methods and tissue culture techniques and will be able to realize how basic research may provide evidence on disease processes such as arteriosclerosis and ciguatera fish intoxication.